1. Field of the Invention
The present invention relates to a surface texture measuring machine and a surface texture measuring method. More specifically, it relates to a surface texture measuring machine and a surface texture measuring method for measuring a narrow area in which a mechanical movement is restricted.
2. Description of Related Art
A surface texture measuring machine for measuring a surface texture (e.g. surface roughness, waviness and profile) and a surface texture measuring method using the surface texture measuring machine have been conventionally known (see Patent Literature 1: JP-A-2000-227327 and Patent Literature 2: JP-A-2001-133247).
The surface texture measuring machine measures a surface texture of a workpiece by tracing a surface of the workpiece with a stylus. Specifically, the stylus is brought into contact with a desired point on the surface of the workpiece and is moved in a predetermined measurement direction along the surface of the workpiece while being in contact with the surface of the workpiece. In accordance with the movement, the stylus displaces in a direction intersecting the tracing direction in accordance with the irregularities on the surface of the workpiece. The displacement is recorded in conjunction with the movement in the tracing direction, whereby the surface texture of the workpiece can be measured.
The surface texture measuring machine includes a drive mechanism for moving the stylus. The drive mechanism typically includes a guide rail that supports an arm provided with the stylus at an end thereof in a manner capable of linear movement, a ball screw shaft disposed along a rail, and a drive source such as an electric motor to rotate the ball screw shaft to feed the arm.
Such a drive mechanism inevitably causes a backlash in the ball screw shaft and the like.
In view of the above, an approach section is set at the start of the tracing operation in some of the surface texture measuring machines.
The approach section is a predetermined distance or time period in which the stylus is simply moved (i.e. without measuring) after starting the tracing operation.
After elapsing or passing the approach section, the surface texture measuring machine performs a movement accompanying a normal measurement operation, i.e. the detection of the displacement of the stylus and data processing.
With the presence of the approach section, the backlash of the drive mechanism is eliminated in the subsequent measurement operation, thereby maintaining appropriate relationship between the movement position and the displacement during the measurement operation.
The above-described approach section is typically defined as an approach distance of approximately 0.5 mm. Specifically, an output of an encoder for detecting the movement position is monitored and the approach section is counted as a pulse number of the encoder corresponding to the above approach distance.
No specific limitation has been posed for setting the approach section, but the approach section has been set with a margin sufficient for eliminating the backlash of the drive mechanism and stabilizing the measurement operation.
Incidentally, the above-described surface texture measuring machine is used not only for measuring a surface texture of a continuous surface of a workpiece but also for measuring a narrow area on a workpiece (e.g. a gap between two projections and bottom surface of a groove).
Such a narrow area sometimes is approximately 1 mm in width. In order to measure such a narrow area, the stylus can be miniaturized to ensure the movement area over the entire inner width of the groove and the like.
However, when the above-described approach section is 0.5 mm, only 50% of the bottom surface of the groove of 1 mm width can be measured.
When the approach section is changed to be set short, the distance available for the measurement can be increased.
However, the short approach section accompanies the following disadvantages.
Firstly, since there is no reference value for changing the approach section to be short, repetitive tests are required.
Further, all the measurement operations are conducted with the short approach section. Thus, when an area other than the narrow area is to be measured, adjustment operation for, for instance, changing back to the typical approach section with a margin is required.